This section provides background information related to the present disclosure which is not necessarily prior art.
The lungs are organs that function to exchange CO2 in blood with O2 in air. It is important for the local alveoli of the lungs to be continuously supplied with new O2 and blood. Various methods are used as methods of diagnosing a pulmonary disease, for example, a chronic obstructive pulmonary disease (COPD), such as emphysema or chronic bronchitis.
As an example of such a method, diffusing capacity of the lungs for carbon monoxide (DLco) is a medical test that measures the difference between the partial pressures of carbon monoxide in inspiration and expiration states. However, DLco provides only the average information of pulmonary functions, and neither distinguishes the left and right lungs from each other nor provides information based on the locations of the lungs.
Meanwhile, high-resolution computed tomography (CT) is widely used as a noninvasive means for estimating a change in a pulmonary structure attributable to CODP. For example, as shown in FIG. 1, a lung image is acquired using CT, and an index, such as the percentage of a low attenuation area (LAA %) in the lung image or an emphysema index (ED, related to the loss of pulmonary functions is employed.
Such CT-based LAA % or EI distinctively shows the left and right lungs, and shows the distribution of emphysema at a pixel level. However, only an emphysema image and an EI are not sufficient to provide objective information about the extent and local distribution of emphysema. For example, from a left emphysema image 1a of FIG. 1 and a right emphysema image 1b of FIG. 1, it can be seen that there is a similarity in the EI and that there is a significant difference in the size and distribution of emphysema. Although a doctor may visually and intuitively determine the size and distribution of the emphysema, a problem arises in that the determination is not objective.
Furthermore, since emphysema is indicative of the structural loss of the lungs, the anatomy of the lungs has a correlation with the size and distribution of emphysema. However, a problem arises in that the intuitive interpretation of a lung image or an EI, i.e., an average numerical value, cannot provide sufficient information about the correlation between the size and local distribution of emphysema and the anatomy of the lungs.
The paper “Longitudinal Study of Spatially Heterogeneous Emphysema Progression in Current Smokers with Chronic Obstructive Pulmonary Disease” by Naoya Tanabe, Shigeo Muro, Susumu Sato, Shiro Tanaka, Tsuyoshi Oguma, Hirofumi Kiyokawa, Tamaki Takahashi, Daisuke Kinose, Yuma Hoshino, Takeshi Kubo, Toyohiro Hirail, and Michiaki Mishima discloses a method of measuring LAA % and a yearly change in the type and number of emphysema clusters is disclosed. However, this paper does not disclose a method of classifying emphysema clusters or emphysemas themselves constituting the emphysema clusters according to their size.